1. Field of the Invention
The present invention relates to a method for analyzing an impurity present on the surface of a semiconductor substrate and, in particular, to a method for measuring an amount of impurity on a semiconductor substrate surface at those local areas of a repeated pattern.
2. Description of the Related Art
It has been known that a metal impurity is present on the surface of a semiconductor substrate or a semiconductor wafer and that the metal impurity, even if being very small in amounts, adversely affects the electric characteristics of a device. With a recent tendency toward realizing a high-density device, more and more exacting demand is made for the analysis of an impurity. There is also a high demand for the high-accurate analytical technique.
In the conventional analytical method, a solution for impurity collection, such as an acid solution, is dropped on a whole surface area of a semiconductor substrate or on a nearly liquid-drop-size area on the surface of a semiconductor substrate where an impurity is collected. Then an amount of impurity collected in that solution used is measured by a chemical analytic apparatus such as a flameless atomic absorption apparatus.
It has been known by an accelerated test that, on a semiconductor substrate having a surface pattern similar to a device surface pattern, the surface distribution pattern of an impurity concentration depends upon the surface pattern of the semiconductor substrate. The device surface pattern has become very small with the microminiaturization of the semiconductor element so that the surface distribution pattern of take impurity concentration becomes very small. Recently, the surface pattern of the device is of the order of a micron or submicron.
On the other hand, the surface resolution by the conventional analytical method is of the order of a few cm.sup.2, an ordinary size of to-be-collected liquid drops at best, thus failing to achieve high-accurate analysis.